Arteries considered as a Cause of Animal Heat. 175 



/brmed in the following manner. Having cut off a circular 

 portion of the descending arch of the aorta, about an inch 

 in length, I laid it open and carefully dissected out the ela- 

 stic coat, and taking hold of it by each extremity, I pulled 

 it to and fro with a continuous jerking motion (in imitation 

 of the systole and diastole of the artery) for the space of about 

 a minute, when placing it upon the bulb of a thermometer, I 

 had the satisfaction to find that after it had remained two 

 minutes the mercury had risen as many degrees. On re- 

 moving the thermometer the heat immediately began to di- 

 minish. To be certain that the heat did not arise from any 

 other source than the one in question, I took the precaution of 

 covering my fingers with a double layer of flannel, to prevent 

 the communication of heat from the body : I also covered my 

 mouth with a handkerchief, to guard against the warm breath 

 affecting the thermometer, whilst watching the progress of the 

 experiment. I may likewise state that the experiment was 

 performed in a room without a fire, the temperature of the 

 air at the time being 55°. There were several difficulties to 

 contend with during the investigation, and it was not until 

 after repeated trials that the experiment succeeded to my satis- 

 faction. The chief impediment I think must have been 

 owing to the moisture of the artery, which by its evaporation 

 must have had a constant tendency to carry off the heat. 

 Having however performed the experiment twice consecu- 

 tively in the same satisfactory manner, I think there can be 

 but little doubt entertained as to its conclusiveness. My at- 

 tention was often arrested, whilst conducting the experiments, 

 by the striking mechanical analogies between caoutchouc and 

 the elastic coat of arteries. Like the latter it could be elong- 

 ated to twice its ordinary length, and, on withdrawing the 

 tension, would return to its usual dimension with considerable 

 force and a snapping noise. I was also surprised to find, on 

 slightly drying it, that it would erase black-lead pencil marks 

 from paper without leaving a stain. This latter circumstance 

 is perhaps of trifling importance ; it serves however to show 

 that strong mechanical resemblance may exist between bodies 

 widely differing in their chemical properties. 



From the foregoing observations I think I am entitled to 

 conclude that the whole of the heat developed in the animal 

 (Economy can now be satisfactorily explained. Physiologists 

 have often proved that the greater i)art of animal heat is oc- 

 casioned by the chemical changes which take place in the 

 lungs during respiration; there always remained however a 

 portion which could not be referred to that source, but which 

 can now I consider be fully accounted for by the mechanical 



